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  <title>Qt 4.3: Qt Object Model</title>
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<p>The standard C++ object model provides very efficient runtime support for the object paradigm. But its static nature is inflexibile in certain problem domains. Graphical user interface programming is a domain that requires both runtime efficiency and a high level of flexibility. Qt provides this, by combining the speed of C++ with the flexibility of the Qt Object Model.</p>
<p>Qt adds these features to C++:</p>
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<li>a very powerful mechanism for seamless object communication called <a href="signalsandslots.html">signals and slots</a></li>
<li>queryable and designable <a href="properties.html">object properties</a></li>
<li>powerful <a href="eventsandfilters.html">events and event filters</a></li>
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<li>sophisticated interval driven <a href="timers.html">timers</a> that make it possible to elegantly integrate many tasks in an event-driven GUI</li>
<li>hierarchical and queryable <a href="objecttrees.html">object trees</a> that organize object ownership in a natural way</li>
<li>guarded pointers (<a href="qpointer.html">QPointer</a>) that are automatically set to 0 when the referenced object is destroyed, unlike normal C++ pointers which become dangling pointers when their objects are destroyed</li>
<li>a <a href="metaobjects.html#qobjectcast">dynamic cast</a> that works across library boundaries.</li>
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<p>Many of these Qt features are implemented with standard C++ techniques, based on inheritance from <a href="qobject.html">QObject</a>. Others, like the object communication mechanism and the dynamic property system, require the <a href="metaobjects.html">Meta-Object System</a> provided by Qt's own <a href="moc.html#moc">Meta-Object Compiler (moc)</a>.</p>
<p>The meta-object system is a C++ extension that makes the language better suited to true component GUI programming. Although templates can be used to extend C++, the meta-object system provides benefits using standard C++ that cannot be achieved with templates; see <a href="templates.html">Why Doesn't Qt Use Templates for Signals and Slots?</a></p>
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